| Abstract
| - Oligonucleotides bearing biodegradable phosphate protecting groups have been synthesized on a solidsupport. For this purpose, two dimeric building blocks, viz. 5‘-O-(4,4‘-dimethoxytrityl)-(RP,SP)-OP-[2,2-bis(ethoxycarbonyl)-3-(pivaloyloxy)propyl]-P-thiothymidylyl-(3‘,5‘)-thymidine 3‘-[O-(2-cyanoethyl)-N,N-diisopropylphosphoramidite] (1) and 5‘-O-(4,4‘-dimethoxytrityl)-(RP,SP)-OP-[2-cyano-2-(2-phenylethylaminocarbonyl)-3-(pivaloyloxy)propyl]thymidylyl-(3‘,5‘)-thymidine 3‘-(H-phosphonate) (2), wereprepared. Phosphoramidite 1 was incorporated into an phosphorothioate oligothymidylate sequenceon a base-labile hydroquinone-O,O‘-diacetic acid linker (Q-linker) and on a photolabile 4-alkoxy-5-methoxy-2-nitrobenzyl carbonate linker (11). H-Phosphonate 2 was, in turn, incorporated into anoligothymidylate sequence only on the photolabile linker. Kinetics of the removal of the protectinggroups by porcine liver esterase and subsequent retro aldol condensation/phosphate elimination werethen studied. While the pro-oligonucleotide that contained only one phosphate protection gave thedeprotected phosphorothioate oligonucleotide in a quantitative yield, the enzymatic step was markedlydecelerated upon increasing the number of protection groups, and hence chain cleavage started tocompete.
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